[lwip-users] Data waiting but no recv()

[Josh Rothstein]

Earlier, I had posted about having trouble with creating a Telnet client using FreeRTOS and lwip.  I was using a button on my development board to transmit a fixed message to a Hyperterm server, and after a few transmissions my stack locked up.  It was supposed that my tcpip task was either blocking or being starved.

 

It turns out that the problem was my client’s mishandling of the responses from Hyperterm.  It seems that Hyperterm responds to each message received by replying with two packets.  The first packet contains the first byte of the message it received, and the second packet contains the rest of the message. I was using the Socket API and was never calling recv(). At each press of the button, my receive buffer was filling up and eventually maxing out.

 

I am curious if my lwip implementation (ethernetif) is handling these unhandled packets properly by filling up the buffer and locking up, or if it should be dropping them and continuing.  I had tried to increase all sorts of buffers in the lwipopts.h but never was able to hit the right one that handled these incoming packets.

 

What is the correct way to make sure that my stack does not lock up if I am receiving unexpected data over a connection?  Should I just poll() each time around the loop?  I cannot just place extra recv()s around the loop or else my task will block if no data is waiting.

 

Thanks,

 

 

Josh Rothstein

Embedded Systems Engineer

DCX-CHOL Enterprises, Inc.

12831 South Figueroa Street

Los Angeles, CA 90061-1157

310.516.1692x134